I've tried multiple methods of adding and removing columns to a dataset, but it seems no matter which way I choose I can't get the data to typeset as a table.

Here's my initial dataset:

1) Construct an association using <|#, ... |> syntax (with the Normal form to show that it yields a list of associations):

2) Using Append[]:

3) Using Join[]:

In each case, the dataset returns is typeset as a single row. Can anyone shed some light on as to why? I have a hunch that I'm fighting some kind of internal type system. What's strange is given much simpler datasets, each one of these methods works fine.